Serverless Webpack

A Serverless Framework plugin to build your lambda functions with Webpack.

This plugin is for you if you want to use the latest Javascript version with Babel; use custom resource loaders, optimize your packaged functions individually and much more!

Highlights

• Configuration possibilities range from zero-config to fully customizable
• Support of serverless package, serverless deploy and serverless deploy function
• Support of serverless invoke local and serverless invoke local --watch
• Support of serverless run and serverless run --watch
• Integrates with serverless-offline to simulate local API Gateway endpoints
• When enabled in your service configuration, functions are packaged and compiled individually, resulting in smaller Lambda packages that contain only the code and dependencies needed to run the function. This allows the plugin to fully utilize WebPack's Tree-Shaking optimization.
• Webpack version 3, 4 and 5 support
• Support NPM and Yarn for packaging
• Support asynchronous webpack configuration

For the complete release notes see the end of this document.

Install

$ npm install serverless-webpack --save-dev

or

$ yarn add serverless-webpack --dev

Add the plugin to your serverless.yml file:

plugins:
  - serverless-webpack

Configure

The configuration of the plugin is done by defining a custom: webpack object in your serverless.yml with your specific configuration. All settings are optional and will be set to reasonable defaults if missing.

See the sections below for detailed descriptions of the settings. The defaults are:

custom:
  webpack:
    webpackConfig: 'webpack.config.js' # Name of webpack configuration file
    includeModules: false # Node modules configuration for packaging
    packager: 'npm' # Packager that will be used to package your external modules
    excludeFiles: src/**/*.test.js # Provide a glob for files to ignore

Webpack configuration file

By default the plugin will look for a webpack.config.js in the service directory. Alternatively, you can specify a different file or configuration in serverless.yml.

custom:
  webpack:
    webpackConfig: ./folder/my-webpack.config.js

A base Webpack configuration might look like this:

// webpack.config.js
module.exports = {
  entry: './handler.js',
  target: 'node',
  module: {
    loaders: [ ... ]
  }
};

Alternatively the Webpack configuration can export an asynchronous object (e.g. a promise or async function) which will be awaited by the plugin and resolves to the final configuration object. This is useful if the confguration depends on asynchronous functions, for example, defining the AccountId of the current aws user inside AWS lambda@edge which does not support defining normal process environment variables.

A basic Webpack promise configuration might look like this:

// Version if the local Node.js version supports async/await
// webpack.config.js
const webpack = require('webpack')
const slsw = require('serverless-webpack');
module.exports = (async () => {
  const accountId = await slsw.lib.serverless.providers.aws.getAccountId();
  return {
    entry: './handler.js',
    target: 'node',
    plugins: [
      new webpack.DefinePlugin({
        AWS_ACCOUNT_ID: `${accountId}`,
      }),
    ],
    module: {
      loaders: [ ... ]
    }
  };
})();

// Version with promises
// webpack.config.js
const webpack = require('webpack')
const slsw = require('serverless-webpack');
const BbPromise = require('bluebird');
module.exports = BbPromise.try(() => {
  return slsw.lib.serverless.providers.aws.getAccountId()
  .then(accountId => ({
    entry: './handler.js',
    target: 'node',
    plugins: [
      new webpack.DefinePlugin({
        AWS_ACCOUNT_ID: `${accountId}`,
      }),
    ],
    module: {
      loaders: [ ... ]
    }
  }));
});

serverless-webpack lib export helper

serverless-webpack exposes a lib object, that can be used in your webpack.config.js to make the configuration easier and to build fully dynamic configurations. This is the preferred way to configure webpack - the plugin will take care of as much of the configuration (and subsequent changes in your services) as it can.

Automatic entry resolution

You can let the plugin determine the correct handler entry points at build time. Then you do not have to care anymore when you add or remove functions from your service:

// webpack.config.js
const slsw = require('serverless-webpack');
module.exports = {
  ...
  entry: slsw.lib.entries,
  ...
};

Custom entries that are not part of the SLS build process can be added too:

// webpack.config.js
const _ = require('lodash');
const slsw = require('serverless-webpack');
module.exports = {
  ...
  entry: _.assign({
    myCustomEntry1: './custom/path/something.js'
  }, slsw.lib.entries),
  ...
};

Optional entry overrides

serverless-webpack generates Webpack entries from the handler value by default.

If your handler is different from the webpack entry, e.g. provided by a layer, you may override the generated entry at function level via the entrypoint option in serverless.yml.

functions:
  my-function:
    layers:
      - LAYER-ARN
    handler: layer.handler
    entrypoint: src/index.handler

Full customization (for experts)

The lib export also provides the serverless and options properties, through which you can access the Serverless instance and the options given on the command-line.

The current stage e.g is accessible through slsw.lib.options.stage

This enables you to have a fully customized dynamic configuration, that can evaluate anything available in the Serverless framework. There are really no limits.

Samples are: The current stage and the complete service definition. You thereby have access to anything that a Serverless plugin would have access to.

Both properties should be handled with care and should never be written to, as that will modify the running framework and leads to unpredictable behavior!

If you have cool use cases with the full customization, we might add your solution to the plugin examples as showcase.

Invocation state

lib.webpack contains state variables that can be used to configure the build dynamically on a specific plugin state.

isLocal

lib.webpack.isLocal is a boolean property that is set to true, if any known mechanism is used in the current Serverless invocation that runs code locally.

This allows to set properties in the webpack configuration differently depending if the lambda code is run on the local machine or deployed.

A sample is to set the compile mode with Webpack 4:

mode: slsw.lib.webpack.isLocal ? "development" : "production"

Output

Note that, if the output configuration is not set, it will automatically be generated to write bundles in the .webpack directory. If you set your own output configuration make sure to add a libraryTarget for best compatibility with external dependencies:

// webpack.config.js
const path = require('path');
module.exports = {
  // ...
  output: {
    libraryTarget: 'commonjs',
    path: path.resolve(__dirname, '.webpack'),
    filename: '[name].js'
  }
  // ...
};

Stats

By default, the plugin will print a quite verbose bundle information to your console. However, if you are not satisfied with the current output info, you can overwrite it in your webpack.config.js

// webpack.config.js
module.exports = {
  // ...
  stats: 'minimal'
  // ...
};

All the stats config can be found in webpack's documentation

Node modules / externals

By default, the plugin will try to bundle all dependencies. However, you don't want to include all modules in some cases such as selectively import, excluding builtin package (ie: aws-sdk) and handling webpack-incompatible modules.

In this case you might add external modules in Webpack's externals configuration. Those modules can be included in the Serverless bundle with the custom: webpack: includeModules option in serverless.yml:

// webpack.config.js
var nodeExternals = require('webpack-node-externals');
module.exports = {
  // we use webpack-node-externals to excludes all node deps.
  // You can manually set the externals too.
  externals: [nodeExternals()]
};

# serverless.yml
custom:
  webpack:
    includeModules: true # enable auto-packing of external modules

All modules stated in externals will be excluded from bundled files. If an excluded module is stated as dependencies in package.json and it is used by the webpack chunk, it will be packed into the Serverless artifact under the node_modules directory.

By default, the plugin will use the package.json file in working directory, If you want to use a different package file, set packagePath to your custom package.json:

# serverless.yml
custom:
  webpack:
    includeModules:
      packagePath: '../package.json' # relative path to custom package.json file.

Note that only relative path is supported at the moment.

peerDependencies of all above external dependencies will also be packed into the Serverless artifact. By default, node_modules in the same directory as package.json (current working directory or specified bypackagePath) will be used.

However in some configuration (like monorepo), node_modules is in parent directory which is different from where package.json is. Set nodeModulesRelativeDir to specify the relative directory where node_modules is.

# serverless.yml
custom:
  webpack:
    includeModules:
      nodeModulesRelativeDir: '../../' # relative path to current working directory.

When using NPM 8, peerDependencies are automatically installed by default. In order to avoid adding all transitive dependencies to your package.json, we will use the package-lock.json when possible. If your project is included in a monorepo, you can specify the path to the package-lock.json:

# serverless.yml
custom:
  webpack:
    includeModules:
      nodeModulesRelativeDir: '../../' # relative path to current working directory.
    packagerOptions:
      lockFile: '../../package-lock.json' # relative path to package-lock.json

Runtime dependencies

If a runtime dependency is detected that is found in the devDependencies section and so would not be packaged, the plugin will error until you explicitly exclude it (see forceExclude below) or move it to the dependencies section.

AWS-SDK

An exception for the runtime dependency error is the AWS-SDK. All projects using the AWS-SDK normally have it listed in devDependencies because AWS provides it already in their Lambda environment. In this case the aws-sdk is automatically excluded and only an informational message is printed (in --verbose mode).

The main reason for the warning is, that silently ignoring anything contradicts the declarative nature of Serverless' service definition. So the correct way to define the handling for the aws-sdk is, as you would do for all other excluded modules (see forceExclude below).

# serverless.yml
custom:
  webpack:
    includeModules:
      forceExclude:
        - aws-sdk

Packagers

You can select the packager that will be used to package your external modules. The packager can be set with the packager configuration. Currently it can be 'npm' or 'yarn' and defaults to using npm when not set.

# serverless.yml
custom:
  webpack:
    packager: 'yarn' # Defaults to npm
    packagerOptions: {} # Optional, depending on the selected packager

You should select the packager, that you use to develop your projects, because only then locked versions will be handled correctly, i.e. the plugin uses the generated (and usually committed) package lock file that is created by your favorite packager.

Each packager might support specific options that can be set in the packagerOptions configuration setting. For details see below.

NPM

By default, the plugin uses NPM to package the external modules. However, if you use npm, you should use any version <5.5 >=5.7.1 as the versions in-between have some nasty bugs.

The NPM packager supports the following packagerOptions:

When using NPM version >= 7.0.0, we will use the package-lock.json file instead of modules installed in node_modules. This improves the supports of NPM >= 8.0.0 which installs peer-dependencies automatically. The plugin will be able to detect the correct version.

ESM output

If you need to generate ESM output, and you cannot safely produce a .mjs file (e.g. because that breaks serverless-offline), you can use copyPackageSectionNames to ensure the output package.json defaults to ESM.

custom:
  webpack:
    packagerOptions:
      copyPackageSectionNames:
        - type
        - exports
        - main

Yarn

Using yarn will switch the whole packaging pipeline to use yarn, so does it use a yarn.lock file.

The yarn packager supports the following packagerOptions:

Common packager options

There are some settings that are common to all packagers and affect the packaging itself.

Custom scripts

You can specify custom scripts that are executed after the installation of the function/service packages has been finished. These are standard packager scripts as they can be used in any package.json.

Warning: The use cases for them are very rare and specific and you should investigate first, if your use case can be covered with webpack plugins first. They should never access files outside of their current working directory which is the compiled function folder, if any. A valid use case would be to start anything available as binary from node_modules.

custom:
  webpack:
    packagerOptions:
      scripts:
        - npm rebuild grpc --target=6.1.0 --target_arch=x64 --target_platform=linux --target_libc=glibc

Forced inclusion

Sometimes it might happen that you use dynamic requires in your code, i.e. you require modules that are only known at runtime. Webpack is not able to detect such externals and the compiled package will miss the needed dependencies. In such cases you can force the plugin to include certain modules by setting them in the forceInclude array property. However the module must appear in your service's production dependencies in package.json.

# serverless.yml
custom:
  webpack:
    includeModules:
      forceInclude:
        - module1
        - module2

Forced exclusion

You can forcefully exclude detected external modules, e.g. if you have a module in your dependencies that is already installed at your provider's environment.

Just add them to the forceExclude array property and they will not be packaged.

# serverless.yml
custom:
  webpack:
    includeModules:
      forceExclude:
        - module1
        - module2

If you specify a module in both arrays, forceInclude and forceExclude, the exclude wins and the module will not be packaged.

Local modules

You can use file: version references in your package.json to use a node module from a local folder (e.g. "mymodule": "file:../../myOtherProject/mymodule"). With that you can do test deployments from the local machine with different module versions or modules before they are published officially.

Exclude Files with similar names

If you have a project structure that uses something like index.js and a co-located index.test.js then you have likely seen an error like: WARNING: More than one matching handlers found for index. Using index.js

This config option allows you to exclude files that match a glob from function resolution. Just add: excludeFiles: **/*.test.js (with whatever glob you want to exclude).

# serverless.yml
custom:
  webpack:
    excludeFiles: **/*.test.js

This is also useful for projects that use TypeScript.

Exclude Files with Regular Expression

This config option allows you to filter files that match a regex pattern before adding to the zip file. Just add: excludeRegex: \.ts|test|\.map (with whatever regex you want to exclude).

# serverless.yml
custom:
  webpack:
    excludeRegex: \.ts|test|\.map

Keep output directory after packaging

You can keep the output directory (defaults to .webpack) from being removed after build.

Just add keepOutputDirectory: true

# serverless.yml
custom:
  webpack:
    keepOutputDirectory: true

This can be useful, in case you want to upload the source maps to your Error reporting system, or just have it available for some post processing.

Nodejs custom runtime

If you are using a nodejs custom runtime you can add the property allowCustomRuntime: true.

exampleFunction:
  handler: path/to/your/handler.default
  runtime: provided
  allowCustomRuntime: true

⚠️ Note: this will only work if your custom runtime and function are written in JavaScript. Make sure you know what you are doing when this option is set to true

Examples

You can find an example setups in the examples folder.

Service level packaging

If you do not enable individual packaging in your service (serverless.yml), the plugin creates one ZIP file for all functions (the service package) that includes all node modules used in the service. This is the fastest packaging, but not the optimal one, as node modules are always packaged, that are not needed by some functions.

Optimization / Individual packaging per function

A better way to do the packaging, is to enable individual packaging in your service:

# serverless.yml
---
package:
  individually: true

This will switch the plugin to per function packaging which makes use of the multi-compiler feature of Webpack. That means, that Webpack compiles and optimizes each function individually, removing unnecessary imports and reducing code sizes significantly. Tree-Shaking only makes sense with this approach.

Now the needed external node modules are also detected by Webpack per function and the plugin only packages the needed ones into the function artifacts. As a result, the deployed artifacts are smaller, depending on the functions and cold-start times (to install the functions into the cloud at runtime) are reduced too.

The individual packaging will automatically apply the automatic entry resolution (see above) and you will not be able to configure the entry config in webpack. An error will be thrown if you are trying to override the entry in webpack.config.js with other unsupported values.

The individual packaging needs more time at the packaging phase, but you'll get that paid back twice at runtime.

Individual packaging concurrency

# serverless.yml
custom:
  webpack:
    concurrency: 5 # desired concurrency, defaults to the number of available cores
    serializedCompile: true # backward compatible, this translates to concurrency: 1

Will run each webpack build one at a time which helps reduce memory usage and in some cases impoves overall build performance.

Support for Docker Images as Custom Runtimes

AWS Lambda and serverless started supporting the use of Docker images as custom runtimes in 2021. See the serverless documentation for details on how to configure a serverless.yml to use these features.

NOTE: You must provide an override for the Image CMD property in your function definitions. See Dockerfile documentation for more information about the native Docker CMD property.

In the following example entrypoint is inherited from the shared Docker image, while command is provided as an override for each function:

# serverless.yml
functions:
  myFunction1:
    image:
      name: public.ecr.aws/lambda/nodejs:12
      command:
        - app.handler1
  myFunction2:
    image:
      name: public.ecr.aws/lambda/nodejs:12
      command:
        - app.handler2

If you want to use a remote docker image but still need the webpack process before doing so, you can specify it as indicated below:

# serverless.yml
functions:
  myFunction1:
    image: public.ecr.aws/lambda/nodejs:latest

Usage

Automatic bundling

The normal Serverless deploy procedure will automatically bundle with Webpack:

• Create the Serverless project with serverless create -t aws-nodejs
• Install Serverless Webpack as above
• Deploy with serverless deploy

Run a function locally

The plugin fully integrates with serverless invoke local. To run your bundled functions locally you can:

$ serverless invoke local --function <function-name>

All options that are supported by invoke local can be used as usual:

• --function or -f (required) is the name of the function to run
• --path or -p (optional) is a JSON file path used as the function input event
• --data or -d (optional) inline JSON data used as the function input event

:exclamation: The old webpack invoke command has been disabled.

Run a function with an existing compiled output

On CI systems it is likely that you'll run multiple integration tests with invoke local sequentially. To improve this, you can do one compile and run multiple invokes on the compiled output - it is not necessary to compile again before each and every invoke.

Using the CLI option --skip-build

$ serverless webpack
$ serverless invoke local --function <function-name-1> --skip-build
$ serverless invoke local --function <function-name-2> --skip-build

Using the parameter noBuild

custom:
  webpack:
    noBuild: true

Run a function locally on source changes

Or to run a function every time the source files change use the --watch option together with serverless invoke local:

$ serverless invoke local --function <function-name> --path event.json --watch

Everytime the sources are changed, the function will be executed again with the changed sources. The command will watch until the process is terminated.

If you have your sources located on a file system that does not offer events, you can enable polling with the --webpack-use-polling=<time in ms> option. If you omit the value, it defaults to 3000 ms.

All options that are supported by invoke local can be used as usual:

• --function or -f (required) is the name of the function to run
• --path or -p (optional) is a JSON file path used as the function input event
• --data or -d (optional) inline JSON data used as the function input event

:exclamation: The old webpack watch command has been disabled.

Usage with serverless run (Serverless Event Gateway)

The serverless run command is supported with the plugin. To test a local service with the Serverless Emulator, you can use the serverless run command as documented by Serverless. The command will compile the code before it uploads it into the event gateway.

Serverless run with webpack watch mode

You can enable source watch mode with serverless run --watch. The plugin will then watch for any source changes, recompile and redeploy the code to the event gateway. So you can just keep the event gateway running and test new code immediately.

Usage with serverless-offline

The plugin integrates very well with serverless-offline to simulate AWS Lambda and AWS API Gateway locally.

Add the plugins to your serverless.yml file and make sure that serverless-webpack precedes serverless-offline as the order is important:

plugins: ...
  - serverless-webpack
  ...
  - serverless-offline
  ...

Run serverless offline or serverless offline start to start the Lambda/API simulation.

In comparison to serverless offline, the start command will fire an init and a end lifecycle hook which is needed for serverless-offline and e.g. serverless-dynamodb-local to switch off resources (see below).

You can find an example setup in the examples folder.

By default the plugin starts in watch mode when triggered through serverless offline, i.e. it automatically recompiles your code if it detects a change in the used sources. After a change it might take some seconds until the emulated endpoints are updated.

If you have your sources located on a file system that does not offer events, e.g. a mounted volume in a Docker container, you can enable polling with the --webpack-use-polling=<time in ms> option. If you omit the value, it defaults to 3000 ms.

If you don't want the plugin to build when using serverless-offline, select the --skip-build option.

Custom paths

If you do not use the default path and override it in your Webpack configuration, you have use the --location option.

serverless-dynamodb-local

Configure your service the same as mentioned above, but additionally add the serverless-dynamodb-local plugin as follows:

plugins:
  - serverless-webpack
  - serverless-dynamodb-local
  - serverless-offline

Run serverless offline start.

Other useful options

You can disable timeouts with --noTimeout when using serverless-offline.

If you use serverless offline to run your integration tests, you might want to disable the automatic watch mode with the --webpack-no-watch switch.

Bundle with webpack

To just bundle and see the output result use:

$ serverless webpack --out dist

Options are:

• --out or -o (optional) The output directory. Defaults to .webpack.

Simulate API Gateway locally

:exclamation: The serve command has been removed. See above how to achieve the same functionality with the serverless-offline plugin.

vscode debugging

To debug your functions using serverless invoke local or serverless-offline check this .vscode/launch.json example.

Example with Babel

In the examples folder there is a Serverless project using this plugin with Babel. To try it, from inside the example folder:

• npm install to install dependencies
• serverless invoke local -f hello to run the example function

Provider Support

Plugin commands are supported by the following providers. ⁇ indicates that command has not been tested with that provider.

Plugin support

The following serverless plugins are explicitly supported with serverless-webpack

Plugin	NPM
serverless-offline
serverless-step-functions-offline

For developers

The plugin exposes a complete lifecycle model that can be hooked by other plugins to extend the functionality of the plugin or add additional actions.

The event lifecycles and their hookable events (H)

All events (H) can be hooked by a plugin.

-> webpack:validate
   -> webpack:validate:validate (H)
-> webpack:compile
   -> webpack:compile:compile (H)
   -> webpack:compile:watch:compile (H)
-> webpack:package
   -> webpack:package:packExternalModules (H)
   -> webpack:package:packageModules (H)

Integration of the lifecycles into the command invocations and hooks

The following list shows all lifecycles that are invoked/started by the plugin when running a command or invoked by a hook.

-> before:package:createDeploymentArtifacts
   -> webpack:validate
   -> webpack:compile
   -> webpack:package
-> before:deploy:function:packageFunction
   -> webpack:validate
   -> webpack:compile
   -> webpack:package
-> before:invoke:local:invoke
   -> webpack:validate
   -> webpack:compile
-> webpack
   -> webpack:validate
   -> webpack:compile
   -> webpack:package
-> before:offline:start
   -> webpack:validate
   -> webpack:compile
-> before:offline:start:init
   -> webpack:validate
   -> webpack:compile

Thanks

Special thanks go to the initial author of serverless-webpack, Nicola Peduzzi, who allowed me to take it over and continue working on the project. That helped to revive it and lead it to new horizons.

Release Notes

See the releases section